<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<style>
  body {
    margin: 0;
    padding: 0;
    height: 100vh;
    background-color: black;
    display: flex;
    justify-content: center;
    align-items: center;
  }

  .circle {
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: lime;
    --inner-circle: 2em;
    width: calc(var(--inner-circle) * 2);
    height: calc(var(--inner-circle) * 2);
    border-radius: 50%;
    box-shadow: 0 0 0 calc(var(--inner-circle) - .4em) black, 0 0 0 var(--inner-circle) lime;
    position: relative;
  }

  .circle::before,
  .circle::after {
    content: '';
    position: absolute;
    width: calc(var(--inner-circle) * 2 * 2);
    height: calc(var(--inner-circle) * 2 * 2);
    border: 2px solid lime;
    border-radius: 50%;
    animation: pulse 2s ease-out infinite;
  }

  .circle::after {
    animation-delay: 1s;
  }
  @keyframes pulse {
    from{
      transform: scale(1);
      filter: opacity(.9);
    }
    to{
      transform: scale(2);
      filter: opacity(0);
    }
  }
</style>
<body>
<div class="circle"></div>
</body>
</html>
